Huge Leak

OK, so I bought a Palmer pump, kinda old, but looks to be in great shape. One problem though, I screw in the bottle from the bottom(vertical) and air leaks like crazy from the lower tube out of the front. That would be the tube below the barrel, the one that the pump handle glides on. A friend and I broke it down to a point where we no longer felt safe trying to take out the last piece in that tube (my mind is drawing a blank right now). Any suggestions on how to further break the marker down and what could be leaking?